The invention relates to a control device for vehicular street traffic including at least one signal disc serving as an optical signalling device which can be covered by pivotal slats fastened to a frame.
The invention is useful specifically for traffic lights which control street traffic with the aid of two or three colored signals.
The current consumption of traffic lights, whose optical signalling devices are usually equipped with incandescent bulbs having a power consumption of 75 to 100 Watts, is considerable. If is assumed that the connected load of the traffic light system of a customary street intersection is about 2 to 3.5 kilowatts and, if operation of 16 hours per day is assumed, such a system consumes about 15,000 kilowatt hours of electrical energy per year. This corresponds to the annual consumption of heating for a well insulated single family home.
In the prior art traffic lights, due to the poor efficiency of the incandescent bulbs employed, only a very small portion of the energy consumed is converted to lighting power. Due to their delayed response, fluorescent bulbs--which are more efficient--cannot replace incandescent bulbs. Another drawback is that the visibility of the signals of the prior art traffic lights is poor unless the observer is located precisely within the relatively narrow cone of the bundled green, yellow or red light being sent out. From a side position or in strong sunlight, the signalling devices are often discernible with difficulty or not at all. However, an increase in light intensity must be kept within limits otherwise the light would be blinding at night.
A variable traffic sign is known which includes a signal disc equipped with lettering which can be covered by horizontally placed, pivotal slats (U.S. Pat. No. 3,553,645). The drawback of this arrangement is that the signal disc or, more precisely, the lettering on the disc, is shaded against daylight when the horizontally disposed slats are open. If the light is viewed in close proximity at as steep angle from the ground, the signal disc is inevitably almost completely covered by the slats so that the lettering can no longer be seen. For this reason, therefore, signalling devices equipped with slats have not been used in the past for traffic control.